This invention is concerned with a direct method of producing a slurry composed of ion-exchanged, synthetic mica crystals dispersed in a polar liquid such as water. In particular, it is concerned with a method wherein two distinct operations are performed as part of one continuous step. Thus, a synthetic mica body is simultaneously dispersed in a liquid and subjected to an ion exchange procedure, thereby forming a dispersed slurry directly.
U.S. Pat. No. 4,239,519 (Beall et al.) is directed to the preparation of inorganic gels from which ceramic papers, films, boards, and coatings can be made. The basic method for preparing those gels contemplates three general steps: (1) a fully or predominantly crystalline body is formed containing crystals consisting essentially of a lithium and/or sodium, water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally-compatible species selected from the group of talc, fluortalc, polylithionite, fluorpolylithionite, phlogopite, and fluorphlogopite; (2) that body is contacted with a polar liquid, desirably water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and (3) the solid:liquid ratio of the gel is adjusted to a desired level depending upon the application therefor.
Papers, fibers, films, boards, and coatings are prepared from the gel. To impart good chemical durability thereto, these products are subsequently contacted with a source of large cations, commonly K.sup.+, Rb.sup.+, Cs.sup.+, NH.sub.4.sup.+, H.sub.3 O.sup.+, Ca.sup.+2, Sr.sup.+2, Ba.sup.+2, Pb.sup.+2, Cu.sup.+, Ag.sup.+ or organic polycations. This causes an ion exchange to take place between the large cations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the crystals. Thereafter the ion-exchanged products are dried. Glass-ceramic bodies are statedly the preferred crystalline starting materials for gel formation.
The patent further discloses that the gel formed from the dispersed, synthetic, lithium and/or sodium mica may be ion exchanged prior to article forming. Thus, the gel is mixed with a source of a large exchangeable cation, such as a potassium chloride solution. This permits exchange of the lithium and/or sodium ions with the larger cation, and consequent formation of a floc composed of the ion exchanged mica crystals.
The floc thus formed may be separated from the liquid and processed, as by pressing and firing. Alternatively, it may be redispersed and further treated. Such procedures are described for example in campanion application Ser. No. 471,539, filed in the names of K. Chyung et al. and entitled "Process for Making Thick-Walled Ceramic Bodies from Synthetic Micas."
The process of first disintegrating the synthetic mica to form a gel, and then ion exchanging to flocculate the gel, involves two separate and distinct steps. This is technically effective and facilitates salt removal and washing. Nevertheless, it is time consuming and hence expensive. It would then be desirable to provide a simpler procedure.